Diamondoid compounds can be converted to their aryl-substituted derivatives in two steps by first halogenating the diamondoid compound and then replacing the halogen with an aryl group. The two-step conversion, requiring separation of an intermediate halogenated organic product, is effective on a bench scale, but the necessary intermediate product separation step has proven to be an obstacle to commercialization of the process on an industrial scale. Thus it would be desirable to provide a method for converting non-halogenated diamondoid compounds to their arylated derivatives which could readily operate in a single vessel in the absence of halogenated diamondoid feedstock.
The term "diamondoid" is used in its usual sense, to designate a family of polycyclic alkanes including adamantane, diamantane, and triamantane, as well as the higher analogs and their substituted derivatives, examples of which include ethyl- and methyl-substituted diamondoids. For a survey of the chemistry of diamondoid molecules, see Fort, Raymond C., Adamantane, The Chemistry of Diamond Molecules (1976) as well as U.S. Pat. Nos. 5,019,660 to Chapman and Whitehurst and 5,053,434 to Chapman. Arylated diamondoids are useful as heat transfer fluids, lubricants, traction fluids, and chemical intermediates. Adamantane has been found to be a useful building block in the synthesis of a broad range of organic compounds, as exemplified by the following references.
U.S. Pat. No. 3,457,318 to Capaldi et al. teaches the preparations of polymers of alkenyl adamantanes useful as coatings, electrical appliance housings, and transformer insulation. The process, yielding polymers bonded through the tetrahedral bridgehead carbons, comprises contacting an adamantyl halide in the presence of a suitable catalyst with a material selected from the group consisting of substituted allyl halides and olefins to produce adamantyl dihaloalkanes or adamantyl haloalkanes as an intermediate product. The intermediate product is then dehalogenated or dehydrohalogenated, respectively, to produce the alkenyl adamantane final product.
U.S. Pat. No. 3,560,578 to Schneider teaches the reaction of adamantane or alkyladamantanes with a C.sub.3 -C.sub.4 alkyl chloride or bromide using AlCl.sub.3 or AlBr.sub.3 as the catalyst. The reference describes polymerization through C.sub.3 -C.sub.4 linkages connecting bridgehead carbon atoms in the starting adamantane hydrocarbon; See column 3, lines 35-55, as well as the structural illustrations in columns 3-5. Coupling adamantane nuclei through C.sub.3 -C.sub.4 linkages is quite different than arylating diamondoid compounds, and the illustration bridging columns 3 and 4 of the Schneider patent clearly shows the production of a halogenated product. The Schneider patent further teaches that primary or secondary alkyl halides are distinctly preferred. Column 5 at lines 12-16.
Landa et al. reported preparation of 1-phenyl adamantane in relatively low yield by heating 1-bromoadamantane with benzene and sodium. Chem. Listy, 51, 2335, 1957 (Chem. Abstract 52:6213a); Collect. Czech. Chem. Commun. 24, 93, 1959 (Chem. Abstract 53:7045b).
Settler et al. improved the yield of the 1-bromoadamantane/benzene reaction by using ferric chloride as the catalyst. Chem. Ber. 92, 1629, 1959.
Newman used 1-bromoadamantane, benzene, t-butyl bromide, and aluminum chloride to prepare 1-phenyl adamantane, 1,3-diphenyl adamantane, 1,3,5-triphenyl adamantane, and 1,3,5,7-tetraphenyl adamantane. Synthesis, 692, 1972.
More recently, Pilgram et al. disclosed the use of 1-acetoxyadamantane in the arylation of diamondoids. Eur. Pat. Appl. EP 358,574 (Chem. Abstract 113:58678v); J. Labelled Compd. Radiopharm 1991, 29(7), 841-6 (Chem. Abstract 115:114119u).